Vacuum-tight glass-metal joint for vessels containing cesium vapor



, m u 8 1 m m m m n T -`aa T. M 7 m f S B m m 1 V T 6 L 4/ u 4 m w W. A nl, T 3 4. d e n m 2 4 m 4 m J w InZK/ -II\- LD. L R 2 G n f G I o., I I N wm C.. F W .mw f Y AJM Hum Rm m LST. I NAW. A /////////4/// www GC A .I TS www I O 6 5 Y .F n A? WI I 2 Nov. 4, 1952 Filed vec. 13, 1949 FIG. 3

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` VACUUM-TIGHT- GLASS-METAL JOINT FOR vEssELs CONTAINING cEsIuM VAPOR [lll/[lll] lll/11111111111 1 Jeun Bucher INVENToRs ATTO R N EY -Wilhelm Spnn|er Patented Nov. 4, 1952 UNITEDV STATES PATENT OFFICE n 2,617,068 A, VACUUM-TIGHT GLASS-METAL JOINT FOR YESSELSCQNTAINING nCESIUM VAPQR Wilhelm Spinnlex",'Bonstettenjand Jean Bacher;

Zurich,'SWitzerland, assignors to FK'G 'FritzVv Kesselring Geratebau Aktiengesellschaft, a

Swiss companyI Application December 1 .Our invention relates to vacuum-tight glassmetal ljoints for vessels containing cesium vapor.Y Various. purposes require theuse of cesium-vapor at-relatively high temperatures in `glass ormetalvessels containing no-appreciable quantities yof other gases. For example, cesium Vapor maybe used in electronic rectifier and illuminating tubes ork for other electronic purposes.` Borosilicate glasses, especially the commercially available heat resistant glassv knownu under thetra'dev name Pyrexare known-to be also resistant to cesium vapor and suitable .for manufacture of such -vessels. These .Pyrex glasses are 'borosilioate-v glasses that-resist the attack of cesium even a temperatures of over 150 C.` f- .It Vhas'been-fou-r-id, however, that-in such vesselsthe glass-metal joints, forinstance the necessary electrode lead-ins, are considerably moreY subject to corrosion than are the glass and metal parts themselves.- rIhis is due tothe action of the It is an objectof our invention to provide vessels containing-cesiumvapor, and:v particularly cesiumf'yaporous thermionic discharge vessels, with glass-toemetal fusion joints or sealscapa'ble ofwithstanding deterioration byf'cesium attack during a useful life period ,ofsuch-considerable length as needed for a commercial and economical application'of such vessels.,

Tothis end, andin accordance with the invention, .at least that portion of' the joint that is in" Contact with thecesiumvapor consists of a fusion of oxidized molybdenum to the cesium-proof glass 3, 1949,seria1No."i32,644 In Switzerland December 1.5, 1948 3 Claims. (Cl. 313-227) and the'thermal design of the vessel is suchas to prevent any-continuous heating above 280 C. of those points of -fusion that are in contact with the cesium vapor.

For further explanation it should be pointed out that it has been found that molybdenum, when fused to borosilicate glasses, and in particular to the above-mentioned Pyrex glass forms an intermediate layer resistant to the action of cesium vapor.' Fused PyrexWmolybdenum joints at temperatures of about 200 C., for instance,.are not attacked by cesium Vapor -even after several'thousand hours of service However,v further investigations have shown that at'temperatures higher than 280 C. even fused molybdenum-borosilicateglass Y joints aret destroyed by cesium Vapor.Y At a temperature of 340 C. such a fused joint of 10 mm. length is destroyed overits entire lengthafter one hours exposure to the action of cesium Vapor, the molybdenum oxide in the vacuum-proof sealing zonef being reduced by this action. At'a temperature of 320 C., on the other hand, the depth of penetration of ithe 'corrosion phenomena along the fusedl layer amounts to-only 1 mm. per 50 hours.

The corresponding figure for temperatures of 300 Cuis l mm. depth of lpenetration per 160 hours.

At lower temperatures the susceptibility of the fused jointsto cesium Vapor declines rapidlyf no appreciable destruction at the point of fusionY being'observabl'e at 280 C. even after several thousand' hours of service.

The designexpedients needed to prevent heating ofthe-points of; fusion to temperatures ex oeedingl 280 C. mayconsist, for instance, in fa-i cilitating the conduction of heat from the points ofrfusion, 'either by giving the metal parts suiti ably' largecross-sectional areas or by "providing special cooling devices-for the points of fusion; moreover, the arrangement of the points offusiorrV within the vessel, and the conditions `of' opera-f' tion of the latterycan easily be so chosenthatthe points-'of fusion do not heat up to temperatures exceeding 280 C.

If .the fusing ltechnique employed is` -cor'- rect,'such fused; joints can* be produced withv` sumcient strength for-many purposes in' spite-'of ythe difference inthe coefficients' of expansion-.-

Where metalfrodfinleads are exposed to *pare* ticularlyhigh temperatures, it may be of advan-Y tage to'make' the metal rod mainlybf ametal' whose* coefficient' of fther'mal expansion rap,-

rproachesmor'e closely that of the glass used: -In' this 'case itis--neces'sar'y to make 'at' least" theI cesium-exposed portion of-the lead-in rod bf: molybdenum. However, such a lead-'inrodfma'y" instead -be provided with a lmolybdenum coat at' r 'least at the end that projects-into the"cesium'' discharge ltube, Fig. 2 shows, also in section, a partial view of a cesium-vaporous discharge tube with a lead-in seal and another fusion joint according to the invention, Figs. 3 and 4 are sectional views o1" respective modied electrode lead-in portions of such tubes, and Eig. 5 shows in cross section an example of a complete rectifier tube to which the invention -is applied.

The cesium vapor lled tube according to Fig. l has an envelope portion I consisting of the above-mentioned heat-resistant borosilicate glass. This envelope portion has a stud I3 of enlarged thickness at the place where it is traversed by an electrode lead-in rod l I of molybdenum. The molybdenum rod and the glass body are joined together by an intermediate fusion layer I2 of glass-molybdenum oxide as described in the foregoing.

The tube shown in Fig. 2 has a vessel 2| of znodlybdenum containing cesium vapor but no other gases or vapors. Part of the vessel envelope consists or" a plate 22 of borosilicate glass and is traversed by an electrode lead-in 23 consisting of a molybdenum rod and sealed to the glass plate by an intermediate molybdenumoxide-glass fusion layer 25 as described previously. The vacuum-tight molybdenum-glass joint produced by fusion of the glass plate 22 to the vessel 2i is designated by the numeral 24. It is also possible to use some other metal for the wall of the vessel, in which event, however, it would be necessary to provide a junction member of molybdenum at the point 24 on the metal vessel, the junction member being in turn fused to the glass plate 22.

The glass-metal lead-in joint shown in Fig. 3 is part of a vessel containing cesium vapor. The illustrated part 3! of the vessel consists of the above-mentioned borosilicate glass. The space above part 3| is deemed to be the interior of the vessel, and the space below part 3I is the exterior space. A molybdenum in-lead rod 32 is fused to the glass part 3| by an intermediate layer 33. At point 34 a rod 35 of some other metal, such as tungsten, Whose coefficient of expansion approaches more closely that of this particular glass, is welded to the molybdenum rod 32, so that the fused joint 33 is mechanically stable even when subjected to extremely high temperature. Since the fused molybdenum-glass joint in contact with the cesium-vapor is resistant to the vapor, the fused tungsten-glass joint 36 cannot be attacked by the cesium.

The cesium-vaporous tube partially shown in Fig. 4 has a lead-in rod consisting of a core 4I of a metal, such as tungsten, whose coefficient of expansion approaches that of the borosilicate glass 42. The core 4I is covered with a coating 43 of molybdenum, which can be produced, for example, by sintering powered molybdenum. This molybdenum coating, when fused to the glass body 42, forms an intermediate layer 44 resistant to the cesium vapor within the vessel.

Fig. shows a rectier tube whose evacuated envelope I consists of a cesium-resistant borosilicate glass and contains a small quantity of metallic cesium. Disposed in the envelope is a helical cathode lament 2 of tungsten, and an anode 3 composed of sheet metal parts of molybdenum. The two inleads 4 of the lament circuit and the anode lead 5, all three consisting of molybdenum, are fused and sealed together with the glass envelope in accordance with the invention. The entire structure is surrounded by a metal cylinder 3 with cover plates 'I of a temperature-resistant insulating material. The filament terminal pins 8 are mounted on one of the insulating plates 1. The anode terminal 9 is cup shaped and mounted on the other insulating plate 1. The coldest spot of the glass envelope reaches a temperature of at least C. when only the lament heating current is switched in. The diameters of the cathode and anode inleads and the radiating surface of the anode are so large as to keep the operating temperature of the fusion seals at 4 and 5 below 280 C. under full anode load.

We claim:

1. A thermionic discharge device comprising, in combination, a sealed envelope containing cesium vapor and having an envelope portion of cesium-resistant borosilicate glass, a vacuumproof glass-to-metal fusion seal forming part of -said portion and being exposed to said cesium vapor, said seal having a lead-in wire of molybdenum and a glass-molybdenum oxide fusion zone joining said borosilicate glass with said wlre.

2. With an electronic discharge device having an envelope structure containing cesium vapor, in combination, a vacuum-tight seal forming part of said envelope structure and having a portion exposed to said cesium vapor, said seal portion consisting of a fusion of cesium-resistant borosilicate glass and a superiicially oxidized conductor of molybdenum, and said device having a heat dissipating capacity adapted to maintain said seal portion at a steady-state temperature of at most 280 C.

3. With a thermionic discharge device having an envelope containing cesium vapor and having an envelope portion of cesium-resistant glass, in combination, a vacuum-proof glass-metal fusion seal exposed to said cesium vapor and comprising an in-lead of molybdenum having a molybdenum oxide-glass fusion zone joined with said vessel portion, said vessel having at said fusion zone a steady-state operating temperature of at most 260 C.

WILHELM SPINNLER. JEAN BACHER.

REFERENCES CITED The following references are of record in theV file of this patent:

UNITED STATES PATENTS Number Name Date 1,320,114 Birdsall Oct. 28, 1919 1,531,966 Mackay Mar. 31, 1925 1,728,822 Charlton Sept. 17, 1929 1,922,535 Erickson Aug. 15, 1933 2,060,043 Cox Nov. 10, 1936 2,190,302 Waldschmidt Feb. 13, 1940 2,515,706 Greiner et al July 18, 1950 FOREIGN PATENTS Number Country Date 109,325 Australia Dec. 6, 1939 354,620 Great Britain Aug. 13, 1931 

1. A THERMIONIC DISCHARGE DEVICE COMPRISING, IN COMBINATION, A SEALED ENVELOPE CONTAINING CESIUM VAPOR AND HAVING AN ENVELOPE PORTION OF CESIUM-RESISTANT BOROSILICATE GLASS, A VACUUMPROOF GLASS-TO-METAL FUSION SEAL FORMING PART OF SAID PORTION AND BEING EXPOSED TO SAID CESIUM VAPOR, SAID SEAL HAVING A LEAD-IN WIRE OF MOLYBDENUM AND A GLASS-MOLYBDENUM OXIDE FUSION ZONE JOINING SAID BOROSILICATE GLASS WITH SAID WIRE. 